In a shop it is frequently necessary to move a heavy piece of machinery a limited distance. To accomplish this it is known to provide the piece of machinery or the platform on which it is mounted with a so-called stepper that allows the piece of machinery to be moved from place to place horizontally. Such a stepper need not be capable of producing a high displacement speed, but must be capable of lifting a large load and displacing it surely and steadily.
A typical stepper is shown in our German Pat. No. 2,129,197. This arrangement has a platform that normally stands on its own legs, but has underneath itself a frame that can shift relative to the platform and that carries a plurality of upright and vertically extensible legs. These legs can be expanded downwardly, normally by pressurization of hydraulic cylinders in them, to lift the platform off the posts on which it is normally supported so that it is supported only on these extensible legs. Then another hydraulic cylinder can shift the platform relative to the frame carrying these legs so that the platform is stepped horizontally. The legs can be retracted to set the platform back down again on its posts and the frame is then shifted back to its original position, whereupon the cycle can be repeated for another step of the platform.
In this system the expansible legs are rigidly fixed on the shiftable frame underneath the platform. Thus they expand along perfectly parallel axes that are perpendicular to the displacement direction and that are all rigidly fixed relative to one another. The disadvantage of this system is that if one leg expands at a rate that is different from any of the others the frame will be twisted considerably. The same will occur if any of the cylinders used for shifting the frame relative to the platform operates at a speed that is greater or less than any of the others, or if the underlying floor or terrain is not perfectly planar. As a result the frame and other associated elements must be built extremely robustly in order to withstand these twisting forces, and control systems must be provided to ensure uniform operation of the various legs.
Another system is shown in German utility model 6,751,750, but here the legs are suspended by ball or knuckle joints directly on the platform and each expansible leg can have its lower end displaced horizontally relative to its upper end by means of a respective double-acting cylinder, with the various cylinders arranged at different angles. The disadvantage of this system is that the machine being displaced will move in short arcs, rather then simply be lifted, transported horizontally, and then dropped with each step. In addition the strain on the cylinders that horizontally displace the lower ends of the expansible legs is considerable, so that these elements must either be very heavily dimensioned or replaced frequently. Finally, the above-given disadvantages of canting or twisting of the structure in the event that some of the cylinders do not operate at the same speed as the others is also present in this system.